Glycans in magnetic resonance imaging: determinants of relaxivity to smart agents, and potential applications in biomedicine.

Carbohydrate chemistry and glycobiology have become a "hot" subject. These extensive, complex structures serve essential roles in cell surface phenomena, but we are only beginning to understand what some of these functions are; any advances in the development of synthetic and/or analytical tools for glycobiology are extremely useful for our understanding of the roles of carbohydrates in biology, and as biomarkers of physiological/pathological states. This review provides an outlook of the potential of carbohydrate chemistry/biology in magnetic resonance imaging (MRI), a major important and prominent technique in diagnostic clinical medicine and biomedical research. During the last 30 years, MRI has developed from an intriguing research project to an essential diagnostic method in the clinic. Although MRI contrast in endogenous tissues provides excellent sensitivity for detecting subtle changes in anatomy and function, MRI still has poor specificity for attributing image contrast to specific biological processes. To overcome this limitation, MRI methods are being developed that induce changes in MR image contrast in response to molecular compositions and functions that serve as early biomarkers of pathologies. Carbohydrates with their intriguing chemistry, not only can provide structures for novel MRI probes for imaging specific biological processes, but can themselves provide novel targets/biomarkers. For example, the glycan structure can simply provide a molecular scaffold for modulating the physicochemical properties of the imaging contrast agent, or can be used for the design of novel MR agents with the ability to disclose relevant physiological or pathological cellular events.